Climatological features of blocking anticyclones: a study of Northern Hemisphere CCM1 model blocking events in present-day and double CO2 concentration atmospheres |
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| Authors: | A R Lupo R J Oglesby I I Mokhov |
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| Institution: | (1) Department of Earth and Atmospheric Science, Purdue University, West Lafayette, IN 47907-1397, USA, US;(2) Institute of Atmospheric Physics, Russian Academy of Sciences, 3 Pyzhevsky, Moscow 109017, Russia, RU |
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| Abstract: | Using output made with the National Center for Atmospheric Research (NCAR) Community Climate Model Version 1 (CCM1), the
characteristics of blocking events over the Northern Hemisphere in a ten-year present day control simulation with a CO2 concentration of 330 ppm were compared to those in a previously analyzed observational three-year climatology. The characteristics
of blocking events in a double present-day CO2 concentration simulation were then compared to those in the control simulation in order to evaluate how these characteristics
might change in an increased CO2 atmosphere. The results demonstrated that in the Northern Hemisphere the CCM1 correctly simulated many characteristics of
blocking events such as average annual number of occurrences, annual variations is size and intensity, and preferred formation
regions. A more detailed analysis (i.e., by region and season) revealed some differences between the CCM1 and observed blocking
events for characteristics such as mean frequency of occurrence, intensity, size and duration. In addition, the model failed
to capture adequately the occurrence of blocking events over the western Asian continent. A comparison of the double CO2 concentration run to the control showed that, in general, blocking events were more persistent and weaker, but of similar
size in the increased CO2 atmosphere. Also, some statistically significant regional and seasonally dependent changes were found in the frequency of
occurrence, duration, and intensity. Finally, a correlation between block size and intensity, significant at the 99% confidence
level, was found in each climatology. This result is similar to a correlation found in the analysis of observations.
Received: 8 May 1995 / Accepted: 20 September 1996 |
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